PP 1 Cell Injury And Death Flashcards
2 causes of cell injury
Environmental
Non environmental
Environment cause of cell injury
Hypoxia
Toxins/poisons
Immune mediated
Physical agents
Infection
Nutritional/dietary
Non environmental causes of cell injury
Genetics
Ageing
Hypoxia meaning
Oxygen deprivation
Causes of hypoxia
Hypoxaemic hypoxia
Anaemic hypoxia
Ischaemic hypoxia
Histotoxic hypoxia
What is hypoxaemic hypoxia?
Arterial content of O2 is low
What is anaemia hypoxia?
Example
Decreased ability of haemoglobin to carry oxygen
e.g. carbon monoxide poisoning
What is ischaemic hypoxia?
Interruption of blood supply
What is histotoxic hypoxia?
Inability to utilise O2 due to disabled oxidative phosphorylation enzyme
How long does it take for neurones to be affected by hypoxia?
A few minutes
why is CPR needed ASAP in cardiac arrest?
Neurones are affected by hypoxia after a few minutes
To prevent brain damage
How long does it take for skeletal muscle to be affected by hypoxia?
A few hours
Examples of toxins
Poison
Pollutant
Insecticides
Herbicides
Asbestos
Alcohol
Drugs
What is a hypersensitivity reaction?
Example
Injury secondary to excessive immune reaction to a non self antigen
E.g. anaphylaxis
Physical agents examples
Trauma
Extreme temp. - frost bite, burns
Electric currents
Radiotherapy
Types of microbes
Bacterial
Viral
Parasitic
Fungal
Nutritional/dietary issues which can cause cell injury
Obesity
Anorexia
Dietary deficiency or excesses - B12/folate/vit D/fat
Issues due to genetics/ageing
Inborn errors of metabolism
Enzyme deficiencies
Dysfunctional proteins
What happens in reversible cell damage?
- swelling: due to Na+/K pump failure
- cytoplasmic blebs
- clumped chromatin: due to reduced pH
- ribosome dispersion: lack of ATP to hold together
- membrane remains intact
What happens in irreversible cell damage?
- nuclear changes
- membrane defects > causes lysis of ER
- lysosome rupture
What is cell death due to?
Irreversible cell injury
Types of cell death
Apoptosis
Necrosis
Apoptosis meaning
Individual programmed cell death
Describe apoptosis
Single cell death
Cell shrinks
Plasma membrane preserved
Organelles contract
DNA cleaved between nucleosides
Dead cells taken up by phagocytosis
Pathways of apoptosis
Intrinsic (mitochondrial)
Extrinsic (death receptor)
Intrinsic pathway of apoptosis
Mitochondria released cytochrome C
Activates caspases which induce apoptosis
What are caspases?
Enzymes involved in cell death
Extrinsic pathway of apoptosis
Death receptors attach to cell membrane which activates caspases > apoptosis
What are death receptors secreted by?
T killer cells
Describe necrosis
Grouped cell death
Cell swells
Plasma membrane destroyed
Organelles swell and break down
DNA is degraded randomly
Dead cells start inflammatory process
Characteristic nuclear changes in necrosis
Pyknosis
Karyorrhexis
Karyolysis
What is pyknosis?
Nuclear shrinkage
What is karyorrhexis?
Nuclear fragmentation
What is karyolysis?
Nuclear dissolution
Main types of necrosis
Coagulative
Liquefactive
Other types of necrosis
Caseous
Fat necrosis
Fibrinoid necrosis
What type of necrosis is often a sign of TB?
Caseous necrosis
Describe coagulative necrosis
Solid organs
Retains ghost outline of cells
Protein denaturation > release of proteases
Describe liquefactive necrosis
Damage of loose tissue
Complete loss of architecture
Tissue breakdown due to release of proteases
Often in soft organs within collagenous framework e.g.brain or areas of many neutrophils
Describe fat necrosis
Direct trauma onto fatty areas
Many adipocytes
e.g. Acute pancreatitis
Molecules released by dead cells
Potassium
Myoglobin
Enzymes
Who have high levels of myoglobin?
Extreme sports athletes
Older people after a fall
Due to over worked muscles
What is myoglobin highly toxic to?
Kidneys
What does high levels of myoglobin cause?
Rhabdomyolysis
Sign of rhabdomyolysis
Tea coloured urine
What could tea coloured urine indicate?
Rhabdomyolysis
Gangrene meaning
Necrosis visible to naked eye
Infarction meaning
Necrosis cause by reduction in arterial blood flow
What can ischaemia cause?
Infarction
What can an infarction cause?
Gangrene
Type of gangrene
Dry
Wet
Gas
What is dry gangrene due to?
What type of necrosis is seen?
Due to necrosis being exposed to air
Coagulative necrosis
What is wet gangrene due to?
What type of necrosis is seen?
Due to necrosis being exposed to infection
Liquefactive necrosis
What is gas gangrene due to?
What does it look like?
Where is it commonly seen?
- Due to wet gangrene being infected by anaerobic bacteria
- visible palpable bubbles of gas within tissue
- Often in traffic accidents
Where is gas gangrene often see?
Traffic accidents
Complications of infarctions depend on…
- alternative blood supply?
- speed of ischaemia
- tissues involved
- O2 content of blood
What is pathological calcification?
Abnormal deposition of calcium within tissues
Types of pathological calcification
Dystrophic/localised
Metastatic/generalised
Where does dystrophic calcification occur?
Areas of dying tissues
Atherosclerotic plaques
Within neoplastic growths
Ageing or damaged heart valves
TB lymph nodes
Where does metastatic calcification occur?
Body wide
Hydroxyapatite crystals deposited in normal tissues in cases of hypercalcaemia
Mechanisms of cell injury
- depletion of ATP
- direct mitochondrial damage
- direct membrane damage
- disruption of calcium homeostasis
- oxidative stress (free radicals)
- direct damage to DNA and proteins
How does hypoxia cause ATP deletion?
1- cells deprived of oxygen
2- reduction in oxidative phosphorylation
3- mitochondrial ATP production stops
Effect of reduction in ATP
- Anaerobic glycolysis > decrease in cell pH > affects enzymes
- ATP needed for NA+/K+ pump > cell swelling + Ca2+ enters cells > irreversible cell damage
- Ribosomes detach from ER > reduce protein synthesis
What does a Ca2+ influx cause?
Irreversible cell damage
What does excess calcium activate?
ATPases
Phosphilpases
Proteases
Endonucleases
What do ATPases do?
Catalyses the hydrolysis of the phosphate bond in ATP to ADP
What do endonucleases do?
Breakdown DNA
What is a free radical?
Atom with unaired electron
Is necrosis always only pathological, only physiological or both?
Pathological only
What are free radicals generated in?
Chemical/radiation injury
Cellular ageing
Anti-microbial killing by phagocytosis
Ischaemia-reperfusion injury
What is the most dangerous free radical?
OH° hydroxyl
What do free radicals damage?
Lipid
Protein
DNA
What antioxidants help the body control free radicals?
- free radical scavengers
- ascrobic acid
- glutathione GSH
Enzymes used to control free radicals
- superoxidase dismutase SOD + catalase
- glutathione peroxidase
How does superoxide dismutase control free radicals?
- SOD: 2 superoxides > 2H2O2
- catalase: 2H2O2 > 2H2O + O2
Heat shock protein function
Help repair + refold damaged proteins
Label proteins for degeneration
Infarction meaning
Necrosis due to ischaemia
Describe caseous necrosis
Structureless
Reduced individuality > looks like a clump
Often in TB
What does the body have to control free radical damage?
Heat shock proteins
e.g. ubiquitin
What transport proteins are used to control free radicals?
Iron binds by transferrin
Calcium binds by ceruloplasmin
What are the most common free radicals?
Hydroxyl
Superoxides
Hydrogen peroxide
Where is Liquefactive necrosis often seen?
Often in soft organs within collagenous framework e.g.brain
Areas of many neutrophils
Where does coagulative necrosis occur?
Solid organs
e.g heart, liver, kidneys, spleen
Is there haemorrhage associated with white or red infarcts?
Red
Where do white infarcts occur?
What are they due to?
What shape are they often in?
Is there associated haemorrhage?
- solid organs e.g.spleen, kidney, heart
- occlusion of end artery
- wedge shaped
- no associated haemorrhage
Where do red infarcts occur?
Is there associated haemorrhage?
- organs with dual blood supply e.g. intestines, lungs
- associated with haemorrhage into dead tissue